Strange problem, need help

I came downstairs this morning and fired my st-70s up and one flashed and blew the fuse. I replaced the fuse and turned the amp back on and I get zero bias voltage on all 4 output tubes. All tubes still light up, but there is no sound in either channel and no bias voltage. Please tell me this is something simple.

Ok, so I panicked and posted before I tried changing the rectifier. I swapped the newish Sovtek 5AR4 rectum frier with a used Mullard and the amp is working again. Do these modern rectifier tubes really go out within 6 months or should I be looking for another issue?

Sad to say that nearly all the newer production GZ34 rectifier tubes are not as "robust" as older USA and British GZ34 rectifier tubes. If you get a year out of most of them, then you are doing OK. Of the newer production GZ34 rectifier tubes (JJ, Sovtek and Ruby), I have had better luck with the Ruby. The Ruby is actually a "select" Chinese GZ34 rectifier tube that has been tested for proper output by Ruby in Califiornia. All Ruby's have the output numbers on a white label on the base of the tube.